Treatment of cellulose preparatory to esterification



Patented May 10, 1932 UNETED STATES HENRY DREYFUS, OF LONDON, ENGLAND TREATMENT OF GELL'ULOSE PREPARATOBY T ESTERIFICATION No Drawing. Original application filed April 18, 1923, Serial No. 633,016, and in Great Britain May 24, 1922. Divided and this application filed March 15, 1929. Serial No. 347,456.

This application is a division of my prior application Serial No. 633,016 filed April 18, 1923.

The above application covers esterifying cellulose or its near conversion products with acetic or other fatty acid anhydride in presence of sulphuric acid or otherstrong condensing agent to produce a highly viscous product by means of using acetic acid or other solvent in quantity over six times the weight of the cellulose. r

The subject-matter of the presentapplication relates to a preliminary treatment which may be given the cellulose or cellulose conversion products in order to render them more reactive to the esterification process while substantially preserving the strength of the cellulosic material. While cellulose or its conversion products which have been pretreat-ed according to the process hereinafter described and claimed are especially suitable for esterification according to the process disclosed and claimed in said parent application, nevertheless they may be esterified by other known or new processes of esterification.

While the pretreatment as hereinafter described is carried out by the use of acetic acid, nevertheless, it may be carried out by the use of other fatty acids, such as propionic,

butyric, or formic acid.

In carrying out the invention, the cellulose or conversion product may be first treated with acetic acid alone, either with heating or at ordinary temperature or with cooling,

3 and sulphuric acid or other strong condensing agent, preferably diluted in acetic acid, be then added at ordinary temperature or with cooling or strong cooling, and the acetic anhydride be then introduced to effect the esterification; or the cellulose or conversion product may be first treated with acetic acid alone, either with heating or at ordinary temperature or with cooling, and then the acetic anhydride be added, the sulphuric acid or $5 strong condensing agent being only added afterwards to the preferably cooled mass; or the cellulose or conversion product may be treated with a mixture of acetic acid and sulphuric acid or other strong condensing 5; agent while preferably cooling or strongly cooling, and the esterification be then effected with the acetic anhydride; or the cellulose or conversion product may be introduced into the mixture of acetic acid, acetic anhydride and sulphuric acid or condensing ing agents, cooling to lowtemperatures of for example below 5 C. and preferably'O C. or lower should be employed at the beginning of the esterification or when the cellulose or conversion product comes in contact with esterifying agent and sulphuric acid or strong condensing agent, precooling being preferably employed withthis object.

Further, I may employ for esterification according to the present invention, whether in solution or suspension, cellulose or cellu lose conversion products which have been subjected to pre-treatment of the character hereinafter mentioned, to render them more reactive while substantially preserving the strength of the cellulosicmaterial.

According to such special pretreatment the cellulose or cellulose conversion product may be heated or boiled with concentrated or dilute acetic acid or other organic acids, preferably with the addition of small quantities of sodium acetate or other and suitable neutralizing agents capable of neutralizing any traces of mineral acids that may be present, and which could have a destructive efiect on the cellulose molecule in the hot treatment with organic acid. For example the cellulosic material may be heated with glacial or dilute acetic acid, preferably containing a small quantity of sodium acetate or other suitable neutralizingagent, at temperatures and for times which may vary with the concentration of the acid used, the time of treatment increasing with decreasing con centration of acid and with reduction of temperature. For instance with glacial acetic acid at about 100 C. or at boiling temperature of the acid, the treatment may last about 1 to 6 hours more or less. The pretreatment with acetic or other organic acids may also take place in the cold, though this may prolong the time of treatment.

In any of the forms of pretreatment above referred to the acetic or other organic acid used for the pretreatment may be employed in admixture with diluents not capable of entering into reaction with the cellulose or acid, such as toluol, but with less advantage.

The pretreated material may be used direct for subjectionto the esterifying reaction, but preferably it is washed and dried before it is esterified.

lVhen cellulose or conversion products pretreated as referred to are used for theesteriance with the present invention.

Eaaample 1 100 parts by weight of cellulose, for example cotton, are introduced into a mixture of 800 parts by weight of glacial acetic acid, 15 73-20% of sulphuric acid relatively to the Weight of the cellulose, and about 200 to 250 parts by weight of acetic anhydride, this mixture having been first cooled down to 0.;

the temperature is allowed'to rise gradually, v

cooling being continued until complete solution. -The reaction is complete in about 2 to 6 hours If desired, the temperature towards the end of the reaction may be allowed to rise to 25 or 30 C. or even some what more to finish the reaction. The cellulose acetate obtained is of much higher *5. viscosity than any hitherto known, as is proved by the fact that theacetylation solution obtained is, in spite of the 70% greater dilution, just as viscous as the best acetylation solutions previously obtainable. The product can be isolated and employed as such or be submitted to a secondary or further treatment either in the original acetylation solution or after isolation therefrom. The isolation of the product from the acetylation solution may be effected by precipitating it in water or with water or with diluents such as carbon tetrachloride and so forth.

Ewample 2 about 010 C. or still lower, are introduced 7 200 parts of acetic anhydride, the mass being constantly mixed or Worked while maintaining cooling until complete solution, so that the temperature is only allowed to rise gradually to about 10 to C. If desired, the temperature may be allowed to rise to 25 C. to complete the reaction or even to about C. The acetylation reaction is finished in about 1 to 3 hours.

Instead of introducing the sulphuric acid with the acetic acid in the preliminary treatment, it may be introduced after treatment with acetic acid, with or without cooling, but

preferably with cooling.

Although of particular value in the production of cellulose acetate the pretreatment which forms the subject-matter of the present invention is of value in the production of any of the fatty acid esters of cellulose. The

invention is, therefore, to be regarded aslimited only by the scope of the appended claims- I What I claim and desire to secure by Letters Patent is I 1'. A process of preparing cellulose for acetylation which consists inmixing the cellulose with acetic acid of such strength that the acid crystallizes when cooled and then cooling the mixture until crystallization of the acid has occurred throughout the mass.

'2. A process of preparing cellulose for esterification which consists in mixing the cellulose with acetic acid of such strength that the acid crystallizes when cooled and then cooling the mixture until crystallization of the acid has occurred throughout the mass.

3. A process of preparing cellulose for esterification which consists in mixing the cellulose with glacial acetic acid and then cooling the mixture to a temperature below 10 C.

4. A process of preparing cellulose for esterification which consists in mixing the cellulose with glacial acetic acid and then cooling the mixture to a temperature below 0 C.

5. A process of preparing cellulose for esterification which consists in mixing the cellulose with a mixture of glacial acetic acid and sulphuric acid and then cooling the mixture until crystallization of the acetic acid has occurred throughout the mass.

In testimony whereof I have hereunto subscribed my name.

HENRY DREYF US. 

